The synchrony of prostaglandin-induced estrus in cows was reduced by pretreatment with hCG.

摘要

The aim of this study was to determine the effect of hormonal treatments aimed at synchronizing follicle waves on the synchrony of prostaglandin-induced oestrus. In the 1st of 2 experiments, 73 cows were given the following treatments on day 5 of the oestrous cycle: (1) injected twice with saline 12 h apart (controls); (2) injected with HCG (3000 IU); (3) injected with HCG and bovine follicular fluid (16 ml, 12 h apart). All injections were given intravenously. On day 12, all cows were treated withprostaglandin (500μg cloprostenol). Cows were fitted with heat mount detectors and observed twice a day for signs of oestrus. On day 12, four cows (1 cow each from groups 1 and 2; and 2 cows from group 3) had plasma progesterone concentrations <1 ng/mland were excluded from the analysis. Cows in groups 2 and 3 showed greater variation in the day of occurrence of oestrus (P<0.0007) and a longer (P<0.005) interval to oestrus after prostaglandin treatment (5.9±0.7 and 6.2±0.8 days) than controls (3.4±0.4 days). Plasma progesterone concentration on day 12 was higher (P<0.0001) in both treated groups than in controls (9.4±0.75 and 8.5±0.75 vs. 4.1±0.27 ng/ml), but there was no correlation between plasma progesterone concentration and the interval to oestrus. In the 2nd experiment, 64 cows were treated on day 5 of the oestrous cycle with saline (group 1; controls) or HCG (3000 IU; groups 2 and 3). On day 12, the cows were injected with prostaglandin (500μg for groups 1 and 2 and 1000μg for group 3). Cows in groups 2 and 3 had a more variable day of occurrence of oestrus (P<0.002) and a longer (P<0.05) interval to oestrus (4.2±0.4 and 4.1±0.4 days) than controls (3.2±0.1 days). Plasma progesterone concentration on days 12 and 14 was higher in groups 2and 3 than in controls. Plasma progesterone concentration was nor correlated with the interval to oestrus. The results showed that the reduced synchrony of prostaglandin-induced oestrus after HCG was not due to failure of luteal regression.